JP2012141299A - In-plane capacitance type mems accelerometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an extremely robust and high-performance triaxial accelerometer including both of an in-plane accelerometer and an out-of-plane accelerometer fabricated on a single chip by using a MEMS manufacturing technology.SOLUTION: A structure of the accelerometer includes an in-plane accelerometer with a substrate rigidly attached to an object, and a proof mass 102 formed from an integrally molded material and movably positioned at predetermined distance above the substrate 104. The proof mass 102 includes a plurality of electrode protrusions 116 extending downward from the proof mass to form a gap of varying height between the proof mass and the substrate. The proof mass 102 is configured to move in a direction parallel to the upper surfaces of each of the plurality of substrate electrodes 108, 110 when the object is accelerating, which results in a change in the area of the gap, and a change in capacitance between the substrate and the proof mass. The in-plane accelerometer can be fabricated using the same techniques used to fabricate an out-of-plane accelerometer and is suitable for high-shock applications.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to accelerometers and other force sensing devices, and more particularly to a super proof mass formed from a single piece of material positioned over a plurality of electrodes on a substrate. It relates to a robust in-plane MEMS capacitive accelerometer. As the substrate accelerates, the proof mass moves in a direction parallel to the top surface of the substrate, changing the capacitance between the proof mass and the substrate. This change in capacitance can be used to measure displacement and identify the acceleration of the object to which the substrate is attached.

Description of Related Art Accelerometers are an important element in inertial measurement units (IMUs) commonly used in navigation and guidance systems for all types of vehicles. A typical IMU consists of three equal modules each including a linear accelerometer, a gyro rotational speed sensor, and associated electronics. These three-axis IMUs are used in navigation, guidance and data measurement systems in aerospace applications ranging from aircraft and spacecraft to precision guided missiles and cannonballs. In many of these applications, the IMU is exposed to extreme vibration and shock loads. For this reason, it must be designed to withstand these harsh conditions.

  An inertial measurement device that can withstand severe impact loads is known as a super robust IMU. Such high performance IMUs remain fully functional even when exposed to forces several thousand times that of gravity. The use of high performance accelerometers and other components allows for reliable, consistent and precise guidance of vehicles and auto-propellants that are equipped with IMUs.

  A high performance accelerometer with microgravity resolution, high sensitivity, high linearity and low bias drift is essential for the use of ultra-stubborn IMUs. Traditionally, IMUs included large mechanical accelerometers and conventional rotary gyros. However, the latest IMUs, particularly ultra-rugged and high performance IMUs, are manufactured using micro-electromechanical (MEMS) manufacturing techniques.

  MEMS manufacturing technology plays an important role in ensuring that large masses, large volumes and small damping are simultaneously obtained with accelerometers while achieving microgravity resolution. Silicon capacitive accelerometers have several advantages that make them very attractive for super robust IMUs. The silicon capacitive accelerometer has high sensitivity and good DC response and noise characteristics, low drift, low temperature sensitivity, low power consumption and simple structure. It is advantageous to build a super robust, high performance 3-axis accelerometer on a single chip using MEMS manufacturing techniques. However, this requires assembly of both out-of-plane and in-plane accelerometers on the chip using the same manufacturing techniques.

  Known in-plane accelerometer configurations include MEMS comb finger accelerometers where a sensing interval is formed between the sidewalls and sensing is determined by the magnitude of the sensing interval. A conventional MEMS comb accelerometer is shown in FIG. The accelerometer 700 includes a proof mass or sensing plate 702 that is spring-loaded to two anchors 704 and has a plurality of movable fingers 706. The movable finger 706 is alternately arranged with a plurality of fixed fingers 708 in a state where a side gap is formed between the movable and fixed fingers. The minimum size of the side gap is limited to about 1/10 to 1/15 of the plate thickness based on the aspect ratio of the dry reactive ion etching (DRIE) technique used to manufacture the in-plane accelerometer 700. Is done. This means that the minimum lateral gap of a 75 μm (micron) thick plate is between 5.0 and 7.5 μm. The smallest size possible with existing DRIE technology is the creation of a 10 μm gap. It is impossible to manufacture a MEMS comb finger or an in-plane accelerometer using this technique on a plate having a thickness of 75 μm.

  Other manufacturing techniques combining micromachining and bulk micromachining can be used to reduce the side gap to 1.1 μm. Polysilicon deposition technology is an example. However, the processing flow of these techniques is very complex and results in low yields. Furthermore, the resulting structure is fragile, making it unsuitable for high impact applications. These existing technologies cannot be used to make super robust MEMS accelerometers.

  In addition, non-linearity problems are inherent in the configuration of conventional comb finger accelerometers. In order to improve linearity, the change in the side gap must be limited to a small range resulting in a small differential capacitance output.

  Given these limitations, super robust and high performance 3-axis accelerometers, including both in-plane and out-of-plane accelerometers made on a single chip using the same MEMS manufacturing technology, are desperate. It is sought after. The present invention addresses this need.

  The present invention relates to a system and method for identifying in-plane acceleration of an object. The system and method will be more readily apparent to those skilled in the art from the following detailed description of the invention in conjunction with the following several figures.

  A system for determining in-plane acceleration of an object is disclosed, and is composed of an in-plane accelerometer with a substrate firmly attached to the object and a monolithic material movably spaced a predetermined distance above the substrate. Including a proof mass. A plurality of first substrate electrodes extend upward from the substrate and alternate with a plurality of second substrate electrodes that also extend upward from the substrate. Each substrate electrode has a planar upper surface. The plurality of first substrate electrodes are electrically connected to each other, and the plurality of second substrate electrodes are also electrically connected to each other. The proof mass includes a plurality of electrode protrusions extending downward from the proof mass to form gaps of different heights between the proof mass and the substrate. The first capacitor is formed between the proof mass and the plurality of first substrate electrodes, and the second capacitor is formed between the proof mass and the plurality of second substrate electrodes. When the proof mass is in an equilibrium position, each of the plurality of electrode protrusions is disposed above a part of one first substrate electrode and a part of an adjacent second substrate electrode, When the speed of the object is constant, the object is held in an equilibrium position. The proof mass is configured to move in a direction parallel to the upper surface of each of the plurality of substrate electrodes when the object is accelerating. This causes a change in the area of the gap between the upper surface of each substrate electrode and the proof mass.

  A method for measuring in-plane acceleration of an object is also disclosed. This method is: a robust attachment of the substrate to the object; fixing the proof mass in a balanced position at a predetermined distance above the substrate to form gaps of different heights between the proof mass and the substrate; Forming a first differential capacitor between the proof mass and the plurality of first substrate electrodes, the proof mass and the plurality of second substrate electrodes being alternately arranged on the substrate. Formation of a second differential capacitor between the substrate electrode and the substrate electrode; movement of the proof mass in a direction parallel to the planar upper surface of the substrate electrode from an equilibrium position by applying an acceleration force to the object; Measuring a first change in capacitance in the second differential capacitor; measuring a second change in capacitance in the second differential capacitor; and converting the measured capacitance change into a voltage representative of the acceleration of the object. Using a circuit for the purpose.

  Additional methods for measuring the in-plane acceleration of an object are also disclosed. The method is: a robust attachment of the substrate to the object; the proof mass is constrained to move in only one direction; the proof mass is suspended above the substrate; the proof mass in a direction parallel to the plane above the substrate electrode A plurality of electrode protrusions with each electrode protrusion centered above the two substrate electrodes so that the area between the plane above each substrate electrode and the proof mass changes as the electrode moves Forming a differential capacitor between the proof mass and the substrate, including: moving the proof mass by applying an accelerating force to the object; measuring a change in capacitance between each substrate electrode and the proof mass; Using a circuit to convert the measured change in capacitance to a voltage representing the acceleration of the object; outputting a voltage from the circuit proportional to the change in the area between the plane above each substrate electrode and the proof mass Process.

  In order that those skilled in the art will readily understand how to implement a system and method for determining the in-plane acceleration of an object, a preferred embodiment of the system and method is described in detail below with reference to the following figures: Describe.

1 is a cross-sectional view of an in-plane accelerometer according to the present invention showing a proof mass suspended above a substrate and wrapped with a topping wafer. FIG. 2 is a detailed view of a portion of the in-plane accelerometer shown in FIG. 1 with the proof mass in the initial position. 2 is an additional detail view of the in-plane accelerometer shown in FIG. 1 with the proof mass in a second position after displacement due to acceleration. FIG. FIG. 3 is a circuit diagram showing an equivalent circuit for a capacitor formed by an in-plane accelerometer of the present invention. FIG. 4 is a functional block diagram of the sensor interface circuit of the present invention that receives input from an accelerometer in the form of a capacitance change and converts the input to a voltage output representing the proof mass acceleration. FIG. 6 is a cross-sectional view of an alternative embodiment of an in-plane accelerometer of the present invention showing electrode protrusions on a proof mass formed by a dry reactive (DRIE) process. FIG. 6 is a top view of a prior art in-plane accelerometer with stationary fingers alternately arranged with movable fingers to form side sensing intervals.

  There is an urgent need for a super robust and high performance 3-axis inertial measurement device that includes both in-plane and out-of-plane accelerometers on a single chip. A novel out-of-plane MEMS accelerometer suitable for this purpose is described in US patent application Ser. No. 11 / 978,090, filed Oct. 26, 2007, entitled “Balanced Gas Damped Suspension Accelerometer”. The The application incorporated herein by reference describes a suspended capacitive accelerometer with an asymmetric proof mass. The suspension sensing plate includes a first side that is substantially hollow and a second side that is not hollow. The out-of-plane accelerometer described in this application uses a 75 μm (micron) silicon-on-insulator (SOI) layer as the sensing structure. Such an asymmetric non-hollow / hollow proof mass sensor structure is more sensitive than a surface micromachined oscillating structure because of the relatively thick proof mass and the narrow vertical gap between the proof mass and the substrate of the out-of-plane suspended accelerometer .

  This disclosure describes an in-plane accelerometer that can be manufactured using techniques similar to those used to manufacture out-of-plane suspended accelerometers. An example of this manufacturing technique is also described in US Pat. No. 7,736, entitled “Wafer Processing Flow for High Performance MEMS Accelerometers” issued June 15, 2010, which is incorporated herein by reference. 931.

  This disclosure describes a super robust, in-plane MEMS accelerometer that measures differential capacitance as a proof mass placed above the substrate moves in a direction parallel to the top surface of the substrate. In order to obtain a high performance, super robust and low noise in-plane accelerometer, it is necessary to increase the size of the proof mass, reduce the sensing interval, and reduce the attenuation. However, in processing thick proof mass MEMS, rather than reducing the vertical gap typical for out-of-plane accelerometers, the side gap typical for in-plane accelerometers, as shown in the conventional series accelerometer of FIG. Is much more difficult to reduce.

  The present invention is an offset comb finger and an in-plane accelerometer that can be manufactured using the same technique as that used for manufacturing an out-of-plane accelerometer. In-plane accelerometers may use thick proof masses and vertical gaps that can be made as small as 1.0 μm. The in-plane accelerometer described in this disclosure has a linear change with respect to acceleration, since the change in area is used instead of the change in gap for measuring capacitance. This is also suitable for open loop accelerometer designs. First and foremost, the manufacturing process flow is the same as existing out-of-plane accelerometers that allow the production of in-plane and out-of-plane accelerometers on a single chip using the same manufacturing techniques.

  This embodiment of the in-plane accelerometer is described in detail and an example is shown in the drawing. For purposes of explanation and illustration, but not limitation, a cross-sectional view of an in-plane, offset, finger comb accelerometer is shown in FIG. In-plane accelerometer 100 includes a proof mass 102, a substrate 104 and a topping wafer 106. The topping wafer may be a glass frit that provides impact protection for the proof mass 102 and is bonded to the substrate 104. Fusion or eutectic bonding may be used to adhere the topping wafer 106 to the substrate 104. The accelerometer 100 may also include a guard ring 105 around the proof mass 102. The substrate 104 is rigidly attached to the object and allows the accelerometer 100 to determine the acceleration of the object by measuring the differential change in capacitance between the proof mass 102 and the substrate 104, or a spring 103 or The proof mass 102 is suspended above the substrate 104 by other suitable means. In one embodiment, the proof mass 102 may be movably attached to a wafer that is fused to the substrate 104.

  FIG. 2 is also a detailed view of a portion of accelerometer 100 showing details of proof mass 102 and substrate 104. The substrate 104 may comprise a silicon-on-insulator (SOI) material. As shown, the substrate 104 includes a plurality of first substrate electrodes 108 extending upward from the substrate 104 and a plurality of second substrate electrodes 110 also extending upward from the substrate 104. The first and second substrate electrodes 108, 110 are arranged in an alternating pattern on the substrate 104. In other words, the substrate electrode directly adjacent to each of the first substrate electrodes 108 is one of the second substrate electrodes 110 and the substrate electrode directly adjacent to each of the second substrate electrodes 110 is the first. This is one of the substrate electrodes 108. Each of the first and second substrate electrodes has a planar upper surface 112 that is a predetermined distance above the planar upper surface 114 of the substrate 104. The planar upper surfaces 112 of the first and second substrate electrodes 108, 110 are arranged in parallel to the planar upper surface 114 of the substrate 104. In one embodiment, the substrate electrodes 108, 110 have a height in the range of about 0.5 μm to about 4 μm.

  FIG. 2 also shows a plurality of electrode protrusions 116 that extend downward from the proof mass 102 toward the substrate 104. The proof mass 102 is formed from a monolithic material. In one embodiment, the material is a semiconductor such as silicon. Since the proof mass 102 is formed from a monolithic material, the protrusion 116 is formed by removing the material from the proof mass 102. The protrusions are not separately formed in an integral part of the proof mass 102. Each electrode protrusion 116 has a lower planar surface 118. In the exemplary embodiment shown in FIGS. 1-3, the electrode protrusions 116 make sidewalls on each electrode protrusion 116 at an angle of 54.7 ° to the lower planar surface 118. Formed using a potassium (KOH) etch process. A recess 120 is formed in a region adjacent to each electrode protrusion 116 between, for example, two electrode protrusions 116. The depression 120 includes a planar depression surface 122 that is parallel to the planar surface 118 under the electrode protrusion 116.

  The proof mass 102 of the accelerometer 100 is positioned above the substrate 104 by a predetermined distance so that a gap 124 is formed between the proof mass 102 and the substrate 104. Since the electrode protrusion 116 extends downward and the first and second substrate electrodes 108, 110 are located on the top of the substrate, the height of the gap 124 between the proof mass 102 and the substrate 104 is set to be proof mass 102. Varies along the length L.

  The proof mass 102 is movably disposed above the substrate 104 by one or more springs 103. Spring design is important to obtain high sensitivity and low crosstalk. Crosstalk is unwanted capacitive coupling from one circuit to another. Since the in-plane accelerometer 100 is designed to measure acceleration along a single axis, it is designed to eliminate crosstalk.

  The main contradiction in spring design is the harmony of sensitivity and crosstalk. The spring should be resilient in the x direction and stiff in the z and y directions. As shown in FIG. 2, the x direction extends along the length of the proof mass 102 and is parallel to the planar surface below the electrode protrusion 116. The y direction is perpendicular to the x direction, and the z direction extends straight out of the page as shown in FIG. In order to achieve rigidity in the y and z directions, maintain flexibility in the x direction, and to prevent crosstalk, the spring should be very thin in the x direction and relatively thick in the y and z directions. is there. In one exemplary embodiment, the width of the spring in the x direction is the same as the width of the proof mass 102 in the x direction. In other words, the spring and the proof mass have the same thickness.

  In spring design, the primary mode of the resonant frequency of the spring must be kept away from the secondary and tertiary modes of the resonant frequency. The spring design parameters are shown in Table 1 below.

  As can be seen from the table, the capacitance sensitivity depends on the resonance frequency of the primary mode. The lower the primary mode frequency, the higher the capacitive sensitivity. Crosstalk depends on the resonance frequency of the secondary mode. The higher the secondary mode frequency, the lower the capacitive sensitivity. With fixed capacitive sensitivity, lower crosstalk can be achieved with thinner springs. The minimum width of the spring is limited by the capacity of the manufacturing process used, for example, the aspect ratio of the dry reactive ion etching (DRIE) process.

  When the object to which the substrate 104 is attached is stationary or in an equilibrium position, that is, when the velocity of the object is constant (no acceleration), each of the plurality of electrode protrusions is one of the first substrate electrodes 108. The proof mass 102 is held in place above the substrate 104 by a spring 130 so as to overlap the portion and a part of the adjacent second substrate electrode 110.

  Each of the first substrate electrodes 108 is electrically connected to each other, and each of the second substrate electrodes is similarly electrically connected to each other. As a result, the first capacitor is formed between the proof mass 102 and the plurality of first substrate electrodes 108, and the second capacitor is formed between the proof mass 102 and the plurality of second substrate electrodes 110. The In one exemplary embodiment, the substrate electrodes 108, 110 have a capacitance of the first capacitor when the acceleration of the object is equal to zero, i.e., when the proof mass 102 is in a balanced position. Are arranged symmetrically to be equal to Since both groups of substrate electrodes are fixed, the substrate 104 is accelerated and the proof mass 102 together with the electrode protrusions 116 in the x direction, ie, on the planar upper surfaces 112 of the first and second substrate electrodes. When moving in parallel, the area of the gap 124 and the total capacitance of each capacitor change.

  As shown in FIG. 2, due to the shape and position of the electrode protrusions 116 on the proof mass 102, each first substrate electrode 108 has a planar surface 118 under the electrode protrusions and a first substrate electrode 108. A first capacitance C1 between the planar upper surface 112 and a second capacitance C1 ′ between the planar surface 122 of the depression of the proof mass 102 and the planar upper surface 112 of the first electrode 108. Have Similarly, each second electrode protrusion has a first capacitance C2 between the planar surface 118 below the electrode protrusion and the planar upper surface 112 of the second substrate electrode 110, and a dent of the proof mass 102. A second capacitance C2 ′ between the planar surface 122 of the second electrode 110 and the planar upper surface 112 of the second electrode 110.

  When the acceleration force a is applied to the proof mass 102, the proof mass 102 moves from the equilibrium position shown in FIG. 2 to the second position shown in FIG. As the proof mass 102 moves from the equilibrium position, the capacitance C2 increases and the capacitance C1 decreases due to the region change in the gap 124 between the proof mass 102 and the substrate electrodes 108, 110. On the other hand, as the proof mass moves from the equilibrium position, the capacity C2 'decreases and the capacity C1' increases. In other words, as the proof mass 102 moves in the x direction as shown, the area of the gap 124 between the proof mass 102 and the planar upper surface 112 of the first electrode substrate 108 increases, The gap area between the planar upper surface of the second electrode substrate 110 is reduced.

  The height of the gap 124 changes along the length L of the proof mass 102. For example, as shown in FIG. 2, the gap 124 has a first height h1 between the planar surface 118 under the electrode protrusion 116 and the planar upper surface 112 of the substrate electrodes 108 and 110, and a depression. A second height h 2 may be provided between the planar surface 122 and the planar upper surfaces 112 of the substrate electrodes 108 and 110.

  The second height h2 is much larger than the first height h1. For example, h2 may be 10 to 20 times larger than h1. The capacity decreases with the distance between the electrodes. As a result of the height difference between h1 and h2, capacitance C1 is much larger than C1 'and capacitance C2 is much larger than C2'. Therefore, the total differential change in capacitance is affected by C1 and C2.

  The aforementioned structure of accelerometer 100 has several advantages. First, when a thick proof mass (greater than 50 μm) is used, the small height h1 of the gap 124 is more easily obtained with a known process capability than the side gap of prior art series accelerometers. In addition, there is no problem of stiction at a high G load in the offset comb finger accelerometer 100 described above. The accelerometer 100 is also suitable for use in a device that is more robust and super robust than the horizontal comb structure.

  FIG. 4 shows an equivalent circuit to the circuit created by the in-plane accelerometer 100. As shown, the circuit includes two capacitors. A first capacitor having a capacitance C1 is formed between the proof mass 102 and the first substrate electrode 108. A second capacitor having a capacitance C <b> 2 is formed between the proof mass 102 and the second substrate electrode 110. The first substrate electrodes 108 are electrically connected to each other. Similarly, each of the second substrate electrodes 110 is electrically connected to each other. Therefore, as shown in FIG. 4, the first and second capacitors consist of a series of small capacitors. Capacitance C1 is equal to the sum of the capacities of these individual smaller capacitors, such as C1 = C1.1 + C1.2 +. Here, n is an integer representing the number of first substrate electrodes 108 on the substrate 104. Similarly, the capacitance C2 is the capacitance of each smaller capacitor formed between the proof mass 102 and the second electrode 110, such that C2 = C2.1 + C2.2 + ... + C2.n. Is equal to the sum of Here, n is an integer representing the number of second substrate electrodes 110 on the substrate 104.

  In one exemplary embodiment, the nominal capacitance values of C1 and C2 are the same when the proof mass 102 and the substrate electrodes 108, 110 are arranged symmetrically, ie between the first substrate electrode 108 and the electrode protrusion 116. Each electrode protrusion 116 has the first substrate electrode 108 and the second substrate electrode 110 so that the overlapping region is equal to the overlap between the adjacent second substrate electrode 110 and the electrode protrusion 116. When aligned above, equals about 7.5 pF (picofarad). FIG. 2 shows the proof mass 102 with electrode protrusions 116 arranged symmetrically above the substrate electrodes 108, 110.

  The difference in capacitance values for C1 and C2 may be caused by a weld misalignment between the proof mass 102 and the substrate 104. The current welding deviation tolerance is 5 μm, which means that the nominal capacitance of C1 and C2 can vary from 2.75 to 13.75 pF.

  The total electric capacity Csum of the accelerometer 100 is equal to the sum of the capacity C1 and the capacity C2. Therefore, since the common mode capacitance change of C1 and C2 is canceled, only the differential change is amplified. This means that z-axis crosstalk leading to common capacitance changes is minimized.

  FIG. 5 illustrates the conversion of the measured difference in capacitance between the proof mass 102 and the substrate electrodes 108, 110 into an output voltage representing the acceleration of the substrate 104 and thus the acceleration of the object to which the substrate is firmly attached. 3 is an example of a circuit that may be linked to the in-plane accelerometer 100. As shown in FIG. 5, the circuit may include a built-in capacitor array that may be used to balance C1 and C2 and minimize bias offset. C1_trim provides a trimming range of 0.2 to 10 pF. The capacitor array includes 9 bits of programmability with 19 fF +/− 20% steps. The fully differential input sensing capacitors are as follows: C1T = C1 + C1_trim. C2T = C2 + C2_trim.

  In one exemplary embodiment, the primary natural resonant frequency of the proof mass is 1890 Hz, and the maximum bending of the beam (beam) along the x-axis is about 2.1 μm. Since the tolerance of welding displacement is 5 μm, the minimum overlap between the electrode protrusion 116 and the substrate electrodes 108 and 110 must be greater than 2.1 μm. Therefore, the layout design overlap must be greater than 7.1 μm.

  In one exemplary embodiment, the width of each substrate electrode 108, 110 is 15 μm, and the width of the electrode protrusions 116 is to ensure that the substrate electrodes are covered by the electrode protrusions 116 even with a deviation of up to 5 μm. 20 μm. If the tolerance shift can be reduced, the width of the substrate electrode can also be reduced. In that case, the number of substrate electrodes can be increased, and the sensitivity of the accelerometer 100 is increased. A deviation tolerance of less than 1 μm can be achieved using a weld alignment machine such as the EVG SmartView® automatic adhesive alignment system available from the Australian EV group.

  An alternative design of an in-plane accelerometer according to the present invention is shown in FIG. The in-plane accelerometer 600 includes a proof mass 602, a substrate 604, and a topping wafer 606, similar to the in-plane accelerometer. As shown, the proof mass 602 is movably disposed above the substrate. Similar to the electrodes described with respect to the in-plane accelerometer 100, the substrate 604 is a plurality of first substrate electrodes 608 that are electrically connected to each other and a plurality of second substrate electrodes 610 that are also electrically connected to each other. including.

  Unlike the in-plane accelerometer 100 shown in FIG. 1, the in-plane accelerometer 600 has a plurality of electrode fingers 616 formed by a dry reactive ion etching (DRIE) process rather than potassium hydroxide (KOH). As a result, the side walls of the electrode fingers 616 are more vertical than the 54.7 degree slope. The vertical sidewalls of the electrode fingers 616 help minimize the parallel stray capacitance of C1 and C2. In addition, side protrusions 620 may be added to the structure of accelerometer 600 to prevent the spring from cracking during high impact loads.

  A system and method for identifying in-plane acceleration of an object with reference to the preferred embodiment system is shown and described, but does not depart from the spirit of the invention and its equivalents as set forth in the appended claims Those skilled in the art will readily understand that various modifications may be made to the systems and methods of this disclosure in scope.

Claims (20)

A substrate firmly attached to the object;
Each substrate electrode has a planar upper surface extending from the substrate and alternating with a plurality of second substrate electrodes extending upward from the substrate, and the plurality of first substrate electrodes are electrically connected to each other The plurality of first substrate electrodes, wherein the plurality of second substrate electrodes are electrically connected to each other;
A plurality of electrode protrusions formed from a monolithic material and disposed above a predetermined distance of the substrate and extending downward from the proof mass to form gaps of various heights between the proof mass and the substrate. A first capacitor is formed between the proof mass and the plurality of first substrate electrodes, and a second capacitor is formed between the proof mass and the plurality of second substrate electrodes. Said proof mass to be provided;
In the proof mass, when the proof mass is in an equilibrium position, each of the plurality of electrode protrusions is disposed above a part of one first substrate electrode and a part of an adjacent second substrate electrode. In a state where the object is held in a balanced position when the velocity of the object is constant;
The proof mass is configured to move in a direction parallel to the top surface of each of the plurality of substrate electrodes when the object is accelerating, and the gap between the top surface of each substrate electrode and the proof mass. An in-plane accelerometer that changes the area.   The in-plane accelerometer according to claim 1, wherein the proof mass is formed from monolithic silicon.   The in-plane accelerometer according to claim 1, wherein a capacity of the first capacitor is equal to a capacity of the second capacitor when the proof mass is in the equilibrium position.   2. The in-plane accelerometer according to claim 1, wherein the plurality of electrode protrusions include a plurality of fingers formed using a deep reactive ion etching (DRIE) process such that a side wall of each finger is vertical. .   The in-plane accelerometer according to claim 1, wherein the plurality of electrode protrusions are etched from the material using potassium hydroxide (KOH) such that the sidewalls of the protrusions have an angle of 54.7 degrees. . The proof mass includes a first planar surface formed between each pair of adjacent electrode protrusions and a second planar surface formed on each of the electrode protrusions. The in-plane accelerometer according to claim 1, wherein both the first and second planar surfaces are parallel to the planar upper surface of each substrate electrode.   A first distance between each first planar surface and one corresponding planar upper surface of the substrate electrode is such that each second planar surface and one same plane of the substrate electrode. The in-plane accelerometer according to claim 6, wherein the in-plane accelerometer is greater than a second distance between the upper surface.   The in-plane accelerometer according to claim 7, wherein the first distance is at least 10 times greater than the second distance.   The in-plane accelerometer according to claim 1, wherein the proof mass is maintained in the balanced position by a spring that allows movement only in a direction parallel to the upper planar surface of the substrate electrode.   The in-plane accelerometer according to claim 9, wherein the crosstalk of the spring in a direction perpendicular to the planar upper surface of the substrate electrode is less than 3%. The in-plane accelerometer according to claim 1, wherein the proof mass has a thickness of 75 μm.   The in-plane accelerometer according to claim 1, wherein the height of each substrate electrode is between 2 μm and 4 μm.   The in-plane accelerometer according to claim 1, further comprising a guard ring around the proof mass.   The in-plane accelerometer according to claim 1, further comprising a topping wafer configured to provide impact protection for the proof mass.   The in-plane accelerometer according to claim 1, wherein the proof mass is movably attached to a wafer welded to the substrate. Rigid attachment of the substrate to the object;
Fixing the proof mass to a position a predetermined distance above the substrate to form gaps of different heights between the proof mass and the substrate;
Forming a first differential capacitor between the proof mass and a plurality of first substrate electrodes, wherein the first substrate electrode and the second substrate electrode are alternately disposed on the substrate; Forming a second differential capacitor between the mass and a plurality of second substrate electrodes;
Movement of the proof mass from an equilibrium position in a direction parallel to the planar upper surface of the substrate electrode by applying an acceleration force to the object;
Measuring a first change in capacitance in the first differential capacitor;
Measuring a second change in capacitance in the second differential capacitor;
A method of measuring in-plane acceleration of an object comprising using a circuit for converting the measured change in capacitance into a voltage representative of the acceleration of the object.   The method of claim 16, comprising a summation in the circuit of the first change in capacitance and the second change in capacitance.   17. The method of claim 16, wherein the circuit is used to amplify a differential change and to minimize a common capacitance change measured with the first and second capacitors.   The forming step of the first differential capacitor and the second differential capacitor comprises centering an electrode protrusion of the proof mass between each pair of adjacent first and second substrate electrodes. 16. The method according to 16. Rigid attachment of the substrate to the object;
Suspension of the proof mass above the substrate, the proof mass being constrained to move in only one direction;
When the proof mass includes a plurality of electrode protrusions, each electrode protrusion being centered on two substrate electrodes, and the proof mass moves in a direction parallel to a planar surface on the substrate electrode Forming a differential capacitor between the proof mass and the substrate such that the area between the planar surface on each substrate electrode and the proof mass changes;
Movement of the proof mass by applying acceleration force to the object;
Measuring the change in capacitance between each substrate electrode and the proof mass;
Using a circuit to convert the measured change in capacitance into a voltage representative of the acceleration of the object;
A method for determining in-plane acceleration of an object comprising outputting a voltage from the circuit that is proportional to the change in the area between a planar surface on each substrate electrode and the proof mass.

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